This invention relates to orthodontic appliances, particularly to orthodontic brackets of the type which are bonded to the external surface of the user's teeth.
Orthodontic brackets which are fastened to the surface of the wearer's teeth by being bonded directly thereto have become quite common. These brackets are typically attached to the outer surface of a pad having an opposite surface configured to generally conform to the shape of the wearer's tooth. This inner, or tooth abutting, surface of the bracket pad is adapted to be attached to the wearer's tooth, such as by adhesive.
One problem with using these bonded orthodontic brackets is a propensity of the pads to break away from the tooth. Among the ways to increase the bonding strength between the adhesive and the bracket is to form the pads with holes through their thickness. This allows adhesive to flow from the tooth abutting surface of the bracket pad, through the hole and on to the outer surface of the bracket pad. In this manner, the adhesive will form a strong mechanical bond between the bracket pad and tooth. However, it has been found that the adhesive on the outer surface of the pad can be worn away during brushing and thus lose much of its gripping power. Further, the desire for an intimate bond between the bracket pad and the adhesive is not addressed in this approach.
Another approach for increasing the bonding strength between the adhesive and the bracket is to sandblast the tooth abutting surface of the bracket pad and/or chemically etch the surface to produce bulbous pores on the tooth abutting pad surface. Either or both of these proceedures can be relatively expensive and also fail to significantly increase the total surface area of the pad to which the adhesive can be bonded.
A third manner of increasing the strength of the bond is to incorporate a wire mesh on the bracket pad and the tooth abutting surface. This again is relatively expensive and can result in a bracket which is thicker than desirable.
Examples of orthodontic brackets incorporating the features described above can be found in U.S. Pat. Nos. 3,765,091; 4,068,379; 4,100,678; and 4,165,561.